Fuiman and Ottey Temperature effects on behavior of young Sciaenops ocellatus 



29 



C/5 



.J-*'-- 1 ^ 



Ai*-- 



■f* 



Time Since Transfer (h) 



Figure 3 



Time-course for pause frequency of young red drum Sciaenops 

 ocellatus at two acclimation temperatures. Annotated as in 

 Fig. 1. 



periments and their magnitude varied greatly with 

 fish size. Small fish showed the least difference be- 

 tween controls, with a maximum of 2.2 s. Mean values 

 for medium fish controls differed by as much as 207.2 s 

 during a given time-period (Fig. 5). Overall differences 

 between the control temperatures were significant only 

 for medium fish. 



Pause duration was highest at the start of trials, 

 with longer pauses at 21° C than at 26° C. Pause 

 duration at the lower temperature decreased over 

 time, approaching levels seen at 26° C, but remain- 

 ing above them throughout the experiments (Fig. 5). 

 This temporal trend was supported by a significant 

 effect of time since transfer for medium fish, but a 

 smaller change and greater variability precluded a 



significant comparison for large fish (Table 3). Small 

 fish showed much more subtle effects of transfer, 

 although there was a significant effect of time due 

 to a rising trend at 26° C. Pause duration generally 

 decreased with time, reaching stable values within 

 1.5 h (Fig. 5). Mean differences (high control minus 

 low control) after 2h for small, medium, and large 

 fish were -0.2 (±0.7), -7.7 (±3.9), and -8.3 (±19.2) s, 

 respectively. 



Transfers Upward and downward transfers had little 

 effect on pause duration after about 2h. The initial 

 effect of a 5°C change on pause duration was consis- 

 tent across the size-classes, but its magnitude varied 

 greatly. Generally, an increase in temperature produced 

 initially shorter pauses than in low controls. Down- 

 ward transfer had the opposite effect, relative to high 

 controls; pause duration increased. The medium size- 

 class was affected most strongly (Fig. 6). The shock of 

 an acute temperature drop was apparently more seri- 

 ous than a comparable increase in temperature. All 

 size-classes showed a statistically significant change 

 in pause duration after a drop in temperature, while 

 none of the size-classes were significantly affected by 

 an increase (Table 3). In contrast, temporal differences 

 in pause duration were more prominent in upward 

 transfers, where small and medium fish were signifi- 

 cantly affected. Only medium fish showed significant 

 differences with time in downward transfers, despite 

 numerous significant differences at individual time- 

 periods for small fish (Fig. 6). 



Discussion 



Transient thermal effects 



The most widely accepted model for the time-course of 

 adaptation of physiological rates to temperature change 

 contains three phases (Kinne 1963, Prosser 1964, 

 Precht et al. 1973). An initial shock reaction occurs 

 during the first seconds to minutes, in which the rate 

 overshoots the level expected for the new tempera- 

 ture. Over a period of minutes to hours, the rate re- 

 turns from these extreme values to a stabilized level. 

 The final stage occupies a prolonged period over which 

 the final acclimated level is reached, but this may re- 

 quire weeks or months. This paradigm allows for two 

 general cases. After exposure to a higher temperature, 

 the overshoot for most measures is positive; the rate 

 increases. When the destination temperature is lower 

 than the acclimation temperature, the overshoot is 

 negative (sometimes called an undershoot); the rate 

 drops below that of the stabilized and acclimated lev- 

 els for the colder temperature. 



